This invention relates to organic stripping compositions containing a heat-stable aromatic quaternary ammonium hydroxide useful in removing hydrophilic polymeric organic substances such as photoresists and their residues from inorganic substrates.
During the manufacture of semiconductors and semiconductor microcircuits, materials from which the semiconductors and microcircuits are manufactured are coated with a polymeric organic substance which forms a resist mask after undergoing a photolithographic process. The resist mask is used to protect selected areas of the substrate surface, e.g. silicon, silicon dioxide, aluminum, or copper, etc., from the action of chemicals in both wet (solution) and dry (plasma) forms. In turn, these chemistries interact with the exposed areas of the substrate to carry out desired etch (removal) and deposition (add) processes. Following completion of this operation and after subsequent rinsing or conditioning, it is necessary that the resist mask and any applicable post-etch residue be removed to permit essential finishing operations.
A common method used in removing the cured resist mask from the substrate is by direct contact with an organic stripper. The chemistry of the stripper penetrates the polymer surface and may undergo a reaction to sever cross-linked portions and facilitate the swelling, lifting, and removal from the surface of the inorganic substrate. The protected area of the substrate is then revealed, typically silicon and its native oxide or a hybrid compound semiconductor such as gallium arsenide and may include sensitive metallic microcircuitry, such as aluminum or copper. Prior stripping compositions have usually been less than satisfactory or have the distinct disadvantage of unacceptable toxicity and/or presenting pollution problems from the disposal of such compounds as phenol, cresol, sulfonic acid, chlorinated hydrocarbons.
The efficiency and selectivity of such stripper is extremely desirable. There is need, accordingly, for improved stripping compositions which will remove the polymeric organic substance from the coated inorganic substrate without corroding, dissolving or dulling the surface of the metallic circuitry or chemically altering the inorganic substrate.
Other prior art inorganic stripping compositions for removing polymeric organic substances, for example, comprise aqueous sulfuric acid compositions containing a significant amount of fluoride ion to reduce metallic dulling and corrosion, as exemplified in U.S. Pat. No. 3,932,130. Some photoresist strippers require the presence of fluoride ion stabilizers to prevent metallic, especially aluminum, corrosion and operate at elevated temperatures.
It is an object of this invention to provide an organic stripping composition which operates effectively without containing the prior mentioned toxic substance and at moderate temperatures, to clean effectively and quickly, organic photoresist materials from metallized inorganic substrates. It is also an object of this invention to provide the same organic stripping composition for removing sub-micron films, coatings, and other forms of organo-metallic residue found in and on micro-device structures such as vias (holes) and lines (metal stacks) resulting from plasma-induced etch processes. The removal process of a cured negative-tone novolak or acrylic resin photoresists and in applications following a plasma etch process, the removal of both the resist mask and post-etch residue is conducted without causing substantial etching of the inorganic substrate or the corrosion or dulling of the metallic circuitry present as adjacent structures.